Mr. Cohen comes to the project from George Mason University, where he directs the Roy Rosenzweig Center for History and New Media. In the announcement, John Palfrey, president of the DPLA’s Board of Directors, praised Mr. Cohen’s contributions to libraries and digital scholarship.

“He has led major open-source development projects, helped to digitize important works of culture, supported teachers and students in accessing fantastic digital materials, and written about the importance of libraries, archives, and museums in a digital age,” Mr. Palfrey wrote. (Mr. Cohen was named one of The Chronicle’s top tech innovators last year.)

Mr. Cohen will move to Boston this year to assume his new duties. In an interview, he called the chance to help build the DPLA “one of those once-in-a-lifetime opportunities.” The idea of “a large-scale online library is something truly special for the 21st century,” he said....